This invention relates to a torque management control for an internal combustion engine, and more particularly to a control that achieves high dilution by maximizing exhaust gas recirculation (EGR).
Recirculation of a controlled amount of exhaust gas into the intake air stream of a vehicle engine, via EGR valve control and/or valve overlap control, has been effectively utilized for reducing exhaust gas emissions. Specifically, the recirculated exhaust gas tends to reduce the peak combustion temperature and pressure, which in turn, reduces nitrogen oxide components (NOx) in the exhaust. Some fuel economy improvements are also achieved since EGR tends to raise the intake manifold pressure, thereby reducing the engine pumping losses. However, the usage of EGR has been limited in production vehicles since the exhaust gas displaces oxygen in the air/fuel mixture, which can cause degraded engine performance. For this reason, the fuel economy improvement realized due to EGR has been relatively minor.
The present invention is directed to an improved engine torque management control that coordinates engine throttle, spark and EGR under predefined highly throttled conditions so as to maximize the fuel economy improvement of EGR without degrading engine performance. Under the predefined conditions, EGR is increased to a level that maximizes the fuel economy improvement without causing combustion instability, and the throttle position and spark timing are controlled to compensate for the anticipated torque loss while increasing volumetric efficiency and reducing pumping losses. During idle and steady state cruising operation, EGR is increased, and engine throttle position is controlled to regulate the estimated engine output torque in accordance with the driver requested output torque. During transient torque increases, throttle control alone is used to regulate the output torque, while in transient torque decreases, the throttle position is maintained and spark timing is used to regulate the output torque.